Cooled electrodes for high repetition excimer or molecular fluorine lasers

ABSTRACT

The consumption and/or erosion of electrodes in high repetition rate gas discharge lasers, such as excimer or molecular fluorine lasers, can be reduced using any of a number of temperature regulation approaches described herein. A flow of a cooling medium can be used to remove heat from the electrodes during laser operation, in order to reduce the rate of consumption and/or erosion. The rate of erosion can be controlled by adjusting the rate and/or temperature of the cooling medium flowing through the electrodes, or in bodies in good thermal contact with those electrodes. The cooled electrodes also can function to remove heat from the laser gas, and can have finned surfaces to facilitate such heat removal. Regulating the temperature of the electrodes and laser gas also can function to minimize resonance effects in the laser gas due to the presence of temperature gradients.

CLAIM OF PRIORITY

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/473,758, entitled “COOLED ELECTRODES FOR HIGH REPETITION EXCIMEROR MOLECULAR FLUORINE LASERS,” to Igor Bragin, et al., filed May 28,2003; as well as U.S. Provisional Patent Application No. 60/486,069,entitled “COOLED ELECTRODES FOR HIGH REPETITION EXCIMER OR MOLECULARFLUORINE LASERS,” to Igor Bragin, et al., filed Jul. 10, 2003, each ofwhich is hereby incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the temperature regulation ofelectrodes, such as may be useful for excimer or molecular fluorinelasers operated at high repetition rates.

BACKGROUND

Gas discharge lasers such as line-narrowed and/or line-selected excimerand molecular fluorine lasers are advantageously used in industrialapplications such as optical microlithography for forming smallelectronic structures on silicon substrates. Photoablation andmicromachining applications typically require medium to high powerlasers, which typically include a laser chamber containing two or moregases, such as a halogen gas and one more rare gases. KrF (248 nm) andArF (193 nm) excimer lasers are examples of gas discharge lasers thatare typically line-narrowed and that have gas mixtures, respectively, ofkrypton, fluorine, and a buffer gas typically of neon; and argon,fluorine, and a buffer gas of neon and/or helium. The molecular fluorine(F₂) laser has a gas mixture of fluorine and one or more buffer gases,and emits at least two lines around 157 nm. One of these lines can beselected and narrowed, such that a very narrow linewidth VUV beam isrealized. The laser chamber contains electrodes which are spaced apartby about 12 mm for high repetition rate lasers, such as for example 6kHz lasers. Further, a fan for circulating the laser gas between theelectrodes is installed, as well as a heat exchanger for cooling thelaser gas. A dust precipitator is used in the laser chamber to removedust particles from the chamber. For high repetition rate lasers of 6kHz and higher, the electrodes often experience a relatively short lifetime and tend to degrade laser performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a cross-section view of a laser chamber that can be used inaccordance with various embodiments of the present invention.

FIG. 1(b) is a schematic diagram showing modules of a laser system thatcan be used with the chamber of FIG. 1(a).

FIG. 2 is a cross-section view of the laser chamber of FIG. 1(a) showinga cooling of the anode and cathode in accordance with one embodiment ofthe present invention.

FIG. 3 is a cross-section view of the laser chamber of FIG. 1(a) showinga cooling of the cathode by a separate, channeled cooling body inaccordance with another embodiment of the present invention.

FIG. 4 is a cross-section view of the laser chamber of FIG. 1(a) showinga cooling of the cathode in accordance with another embodiment of thepresent invention.

FIG. 5 is a cross-section view of the laser chamber of FIG. 1(a) showinga cooling of the anode by a channeled cooling body in accordance withanother embodiment of the present invention.

FIG. 6 is a cross-section view of the laser chamber of FIG. 1(a) showinga cooling of the anode in accordance with another embodiment of thepresent invention.

FIG. 7 is a cross-section view of the laser chamber of FIG. 1(a) showinga cooling of the anode and special shape of the anode in accordance withanother embodiment of the present invention.

FIG. 8 is a cross-section view of the laser chamber of FIG. 1(a) showinga cooling of the anode and fins on the surface of the anode inaccordance with another embodiment of the present invention.

FIG. 9 is a cross-section view of the laser chamber of FIG. 1(a) showinga fin structure of the anode in accordance with another embodiment ofthe present invention.

FIG. 10 is a cross-section view of the laser chamber of FIG. 1(a)showing cooling elements outside the laser chamber in accordance withanother embodiment of the present invention.

FIG. 11 is a cross-section view of the laser chamber of FIG. 1(a)showing replacement of the heat exchanger by cooling plates inaccordance with another embodiment of the present invention.

DETAILED DESCRIPTION

Systems and methods in accordance with various embodiments of thepresent invention can overcome deficiencies in existing gas dischargelaser systems by utilizing any of a number of temperature regulationapproaches disclosed herein. For example, a laser chamber can have apair of discharge electrodes that are “cooled” when the laser system isoperating at repetition rates at or above about 4.0 kHz. As an electrodetends to increase in temperature during laser operation, “cooling” of anelectrode as described herein can refer generally to any approach bywhich an amount of heat is removed from that electrode. For instance, anelectrode can be said to be “cooled” if the electrode is only allowed toincrease in temperature to 100° C., but is not allowed to increasebeyond 100° C. due to an amount of heat removal from the electrode. Theamount of heat removed can be varied in order to maintain the electrodeat 100° C., or simply to ensure that the electrode does not exceed 100°C. In one embodiment, a control module can begin a flow of coolantthrough at least one channel in an electrode when the repetition rate ofthe laser nears, reaches, or exceeds about 4 kHz. Alternatively, theflow can remain constant but the control module might lower thetemperature of the cooling media as the repetition rate nears, reaches,or exceeds about 4 kHz. Cooling of the electrodes can improve the lifetime of the electrodes while minimizing acoustic resonance effectsinside the laser chamber. Several exemplary embodiments are disclosedherein which can be advantageous for differing systems and applications.

FIG. 1(a) shows a cross-section 100 of an exemplary discharge tube ofthe prior art, which can be used with various embodiments of the presentinvention. The cross-section shows elements of a typical gas dischargelaser as would be known to one of ordinary skill in the art, including alaser chamber 102, a preionization unit 104 which can include a numberof pre-ionization pins protruding into the laser chamber as known in theart, anode 106 and cathode 108 electrodes, a gas circulation fan 110, anelectrostatic filter 112, a heat exchanger 114, and discharge capacitors116. The direction of gas circulation in the laser chamber is indicatedby reference line 118, which passes from a lower, laser gas portion ofthe laser chamber through a discharge region 120 between the anode 106and cathode 108 electrodes

FIG. 1(b) shows a schematic overview of the modules of an exemplarylaser system 150 that can be used in accordance with various embodimentsof the present invention. The overall system includes a laser chamber152 with a pair of discharge electrodes 154, such as is described withrespect to FIG. 1(a). A solid-state/thyratron pulser module 156 and highvoltage power supply 160 can be used to provide electrical energy incompressed electrical pulses to the preionization and main electrodes154 in the laser chamber 152, in order to energize the gas mixture andgenerate an optical pulse in the chamber. Pulser components for bothsingle and multiple chamber systems are described in pending U.S. patentapplication Ser. No. 10/776,137, entitled “EXCIMER OR MOLECULAR FLUORINELASER WITH SEVERAL DISCHARGE CHAMBERS,” to Sergei V. Govorkov et al.,filed Feb. 11, 2004, as well as pending U.S. patent application Ser. No.10/699,763, entitled “EXCIMER OR MOLECULAR FLUORINE LASER SYSTEM WITHPRECISION TIMING,” to Dirk Basting et al, filed Nov. 3, 2003, both ofwhich are hereby incorporated herein by reference. A processor 168,computer, or control module for the overall laser system can receivevarious inputs, such as a temperature from the cooling module, a drivesignal from a stepper machine, and a status signal from the diagnosticmodule. In response to these and other inputs, as well as anyprogramming or other data, the processor can control various operatingparameters of the system. A diagnostic module 170 can receive andmeasure one or more parameters of the laser system, such as pulseenergy, average energy, and power. The diagnostic module 170 also canmeasure the wavelength of a split-off portion 176 of the main beam 172.The split-off portion can be redirected by optics, such as a beamsplitter 174, capable of deflecting a small portion 176 of the beamtoward a detector of the diagnostic module 170. A resonator cavity canbe defined by a front optics module 164 and rear optics module 162,disposed on either side of the laser chamber 152 containing the lasergas mixture, such that the overall resonator cavity would include thelaser chamber as well as the front and rear optics modules.

In some embodiments a dual chamber system can be utilized, such as aMOPA system as is known in the art and as described in pending U.S.patent application Ser. No. 10/696,979, entitled “MASTEROSCILLATOR—POWER AMPLIFIER EXCIMER LASER SYSTEM,” to Gongxue Hua et al.,filed Oct. 30, 2003, which is hereby incorporated herein by reference.MOPA technology can be used to separate the bandwidth and powergenerators of a laser system, as well as to separately control each gaslaser chamber, such that both the required bandwidth and pulse energyparameters can be optimized. Using a master oscillator (MO), forexample, an extremely tight spectrum can be generated forhigh-numerical-aperture lenses at low pulse energy. A power amplifier(PA), for example, can be used to intensify the light, in order todeliver the power levels necessary for the high throughput desired bythe chip manufacturers. The MOPA concept can be used with anyappropriate laser, such as KrF, ArF, and F₂-based lasers. Further, aMOPA system can utilize separate switch/pulser systems for each laserchamber (for the MO and the PA). In such a MOPA system, the opticsmodules can be positioned on either side of the master oscillatorchamber, and can allow the resultant optical pulse to pass to the poweramplifier.

One of the optics modules 162, 164 can include line-narrowing optics,which can be useful for applications such as photolithography. In otherembodiments, the optics modules may simply include resonator mirrors forlaser systems where line-narrowing is not desired, such as for TFTannealing applications, or where a spectral filter is used that isexternal to the resonator. For an F₂-laser, for example, optics can beused to select one of multiple lines around 157 nm.

An optics control module 166 can be used to control the front and rearoptics modules, such as by receiving and interpreting signals from theprocessor 168 and initiating realignment, gas pressure adjustments, orreconfiguration procedures in response to those signals. The diagnosticmodule 170 can be a wavelength and/or bandwidth detection component suchas a monitor etalon, energy detector, or grating spectrometer. A hollowcathode lamp or reference light source, for example, can be used toprovide absolute wavelength calibration of such a monitor etalon orgrating spectrometer. Halogen gas injections and gas replacementprocedures, as known in the art, can be performed using a gas handlingmodule 158, which can include a vacuum pump, a valve network, and one ormore gas compartments. A laser control computer 168 can communicatethrough an interface 180 with a stepper/scanner computer 182, othercontrol units 184, and/or other external systems.

A cooling module, as discussed elsewhere herein, can be in electricalcommunication with the processor 168, and can be in fluid communicationwith at least one channel in at least one of the electrodes 154, orbodies in thermal contact with those electrodes. The cooling module canreceive a signal from a temperature sensor, or from a processor orsystem computer, indicating the current temperature of at least one ofthe electrodes, the laser gas, and/or the laser chamber, or an amount oftemperature adjustment. The control module, in response to thetemperature signal, can alter the cooling of the electrodes and/or laserchamber by altering a flow of cooling medium through theelectrodes/chamber, such as by altering a temperature or flow rate ofthe medium. The control module can be in fluid communication with a pump(not shown) for creating the flow, and can be in fluid communicationwith a media reservoir (not shown) for storing and/or providing thecooling medium. A heat exchanger (not shown) or other temperaturecontrolling mechanism also can be used to adjust the temperature of thecooling medium entering the electrodes/chamber.

In another embodiment, the cooling module can be replaced by atemperature control or temperature regulation module. Such a module canbe in communication with a fluid temperature regulator, or a source ofwarm and cool fluids, in order to control a temperature of the mediumflowing through the channels of the electrodes and/or additional bodies.If it is desirable to heat an electrode, for instance, such as at thebeginning of a pulse cycle when the electrode is otherwise relativelycool, a heated fluid can be flowed through the channels in order to heatthe electrode. The heating flow can be reduced once the pulsing begins,or once the electrode reaches a certain temperature. A cooling flow thencan begin once the repetition rate reaches a certain level, or when thetemperature of the electrode reaches a predetermined temperature. Insuch systems, the flow can be used to add or remove heat from thesystem, depending upon the state of the system.

Each laser chamber in the system can include at least a pair ofelectrodes for charging the laser gas. Each electrode can include anelectrode body made of an appropriate material, such as brass, which canbe desirable for 1-4 kHz lasers as well as high repetition rate lasersof 6 kHz and higher. Each electrode can have a ceramic spoiler (notshown) as described in pending U.S. patent application Ser. No.10/727,718, entitled “SYSTEMS AND METHODS UTILIZING LASER DISCHARGEELECTRODES WITH CERAMIC SPOILERS,” to Igor Bragin et al., filed Dec. 4,2003, which is assigned to the same assignee as the present inventionand is hereby incorporated herein by reference. The electrode body canhave a “nose” portion on the order of 0.4-1.0 mm in width and 2-4 mm inheight for 1-6 kHz lasers. Lasers with repetition rates of 6 kHz orhigher can utilize a nose portion on the order of 1.0 mm or lower inwidth and about 2.0 mm in height. For lasers of 6 kHz and higher, thegap between the anode and cathode electrodes can be reduced, such asfrom about 16 mm to about 12 mm, in order to reach a stable dischargewith well-defined laser parameters.

One problem with a chamber design such as is shown in FIG. 1(a) is thatthere tends to be a strong erosion or consumption of the electrodes whenthe laser is operated at repetition rates of about 6 kHz and above.Long, continuous operation at such rates can result in a reduction ofthe laser output, or a change in the laser beam parameters, due toelectrode erosion. Electrode erosion also can lead to the shape of thedischarge being increasingly non-uniform, such as a discharge that iswider, narrower, split, or in any other way distorted, such that thequality of the laser beam degrades over time.

One primary cause for the erosion or consumption of the electrodes isthe physical sputtering caused by ions and electrons impinging upon theelectrodes. In order to minimize the amount of sputtering, many systemsutilize electrode materials having high melting points, high hardnessvalues, and/or high conductivity values. Further, reactions of theelectrode materials with halogens present in the laser chamber cancontribute to the consumption or erosion of the electrodes. Where thereactivity with respect to the halogen gases is sufficiently small, thefactors which affect the electrode erosion can include, for example, theresistance to the evaporation and dissipation (changes of the thermalcharacteristics with respect to melting point, boiling point, vaporpressure, etc.) due to sputtering of the electrodes. Another such factoris the mechanical resistance to the thermal fatigue resulting fromlocalized temperature rise of the electrodes, such as is described inU.S. Pat. No. 5,187,716, which is hereby incorporated herein byreference.

Electrodes are typically designed under the assumption that theelectrodes will be operating in a perfectly uniform electric field. Theactual discharges within a gas discharge laser, however, are notperfectly uniform. For instance, during an initial period after thebeginning of the discharge, the discharge can be somewhat concentratednear the region(s) of strongest electrical field. The portions of theelectrodes corresponding to these regions are eroded more quickly,typically into forms corresponding to the actual distribution of theelectric field. Experiments have shown, for at least one system, thatthe consumption or erosion of the anode is much stronger than for thecathode. This observation is reported, for example, in U.S. Pat. Nos.6,560,263 B1 and 5,187,716, each of which is incorporated herein byreference, where it is disclosed that fluorine (F) anions can contributesubstantially to the consumption of electrodes. Attempts to reduce theerosion of the electrodes are disclosed in Patent Application WO03/023910 A2, which is hereby incorporated herein by reference.

Erosion of the electrode material also can result in the production of“dust” in the laser chamber. This dust can degrade the quality of thedischarge, and can contaminate the laser gas. The dust also can collecton the windows of the laser chamber, reducing the output of the chamberand requiring a periodic cleaning and/or changing of the chamberwindows. Reducing the erosion of the laser therefore also can lessensystem downtime by extending the life of the laser gas as well as thetime between cleanings or changing of the chamber windows. Heating ofthe electrodes also can increase the presence of temperature gradientsin the laser chamber, which can cause resonance effects that influencethe laser parameters.

Systems and methods in accordance with various embodiments of thepresent invention can overcome these and other deficiencies in existinghigh repetition rate gas discharge laser systems through a temperatureregulation of at least one electrode in the laser system. Removing heatfrom at least one of the electrodes during laser operation can prolongthe life of that electrode, and can provide for a more stable discharge.Reducing the erosion of the electrode(s) also can lower the amount ofsystem downtime needed to replace laser gas and remove dustcontamination. Several embodiments are described herein through whichelectrode cooling can be accomplished. Cooling approaches describedherein may be discussed with respect to a single laser chamber forsimplicity, but it should be understood that the cooling approachesdiscussed herein can be used equally as well in multiple chambersystems, such as MOPA systems, with each chamber using the same coolingapproach, or with at least some chambers using a combination of mixingapproaches discussed herein. For example, an oscillator chamber mightrequire more or less cooling than an amplifier chamber in the samesystem, such that it might be more efficient to utilize differentcooling approaches for each chamber.

FIG. 2 shows a cooling approach 200 in accordance with a firstembodiment of the present invention. In this embodiment, the electrodes202, 204 in the discharge area of the laser chamber each have at leastone channel, indicated by 206 and 208 respectively, located in the bodyof the electrode through which a cooling medium can flow. The flow ofcooling medium through the channels can function to remove heat from theelectrode bodies. The amount of heat removed can be controlled by thetemperature of the cooling medium, the flow rate of the cooling medium,and the choice of cooling medium itself, such as a flow of water, or anappropriate oil or gas. The flow rates, cooling medium temperatures, andcooling media used can vary by application. The optimal combination canbe determined for each system and/or application through routineexperimentation as would be known to one of ordinary skill in the art.In one embodiment, water is used as a cooling medium and is controlledto be at a temperature in the range of 30-120° C., with a flow rate onthe order of several liters per minute, in order to optimize the amountof heat removal. Each electrode can have multiple channels disposed inthe body of the electrode. There can be a single flow to all of thechannels, a separate flow for each channel, or a number of flows lessthan the number of channels. The location of the channels can beselected to maximize cooling while minimizing thermal gradients acrossthe electrode. For example, in FIG. 2 the flow of gas between theelectrodes would be from right to left through the discharge gap. Inthis case, the initial discharge might tend to push toward the left ofthe gap such that the left half of the electrode might tend to heat morethan the right half. If this is the case, it might be beneficial to movethe channel toward the left side of the electrode in the Figure, orincrease the number and/or density of the channels toward that side ofthe electrode. If multiple flows are being directed through theelectrode, it also might be beneficial to direct the coolest flowthrough the left side of the electrode.

Special fittings can be used in the case of multiple channels, in orderto connect the channels with each other such that a single flow ofcooling medium can be used. Not shown in FIG. 2 are tubes or pipingwhich can be used to connect an inlet side of each channel and an outletside of each channel to a cooling medium source (not shown) and/or drainlocated the outside of the laser chamber 210. The tubes can be connectedvia commercially available fittings to the channels of the electrodes.The connections can be brazed or welded connections, for example. Careshould be taken during the assembly process to ensure the fittings aresufficiently tight, such that no leaks exist through which the coolingmedium could enter the laser chamber. In embodiments where a closedcycle cooling system is used, a reservoir for the cooling medium can beused along with a pump to agitate the cooling medium in the coolingcycle.

Experiments have shown that, for a system in accordance with at leastone embodiment, 2-3 kW of heat needs to be removed from the electrodesduring laser operation at high repetition rates. It therefore can bedesirable to optimize the size and location of the channels in theelectrode, as well as the flow rate and temperature of the coolingmedium flowing through those channels. For example, it can be desirableto place the cooling channels as close as possible to the electrodesurface in order to maximize the amount of heat removal. The coolingmedium also can be cooled before entering the channels of theelectrodes, such as through use of a commercially available heatexchanger. In an embodiment wherein oil is used as the cooling medium,it is possible to reuse the oil from the pulser model to cool theelectrodes. In laser systems where two or more electrode pairs are used,the channels of the anodes and the channels of the cathodes can beconnected by fittings, or each electrode can be individually connectedto the cooling medium. Tubes and fittings used to direct and contain thecooling medium can be selected from a group of materials that areresistant to halogens in the laser gas. Further, these additionalcomponents also are potential sources of contamination of the lasergases within the laser chamber. Contamination of the laser gases duringthe operation of an excimer laser can quench the laser action. Tubes andfittings inside of the laser chamber can be cleaned before use in thelaser chamber in order to prevent contaminants such as hydrocarbons frombeing introduced into the laser chamber.

If the laser system is a multi-chamber system, one, some, or all of thelaser chambers can include a flow of cooling medium through theelectrodes, as described with respect to FIG. 2. In order tosufficiently cool the electrodes, it may be desirable to direct aseparate flow of cooling medium to each chamber, as using the same flowcan cause the medium be heated after each chamber. Alternatively, thesystem can utilize heat exchangers or other cooling methods to removeheat from the flow of cooling medium between chambers, such that asingle flow can be used irregardless of the number of chambers in thesystem. In other systems, it may be advantageous to use differenttemperatures and/or cooling media with each chamber, in order tooptimize operation of each chamber.

FIG. 3 shows a cooling approach 300 in accordance with a secondembodiment of the present invention. In this embodiment only one of theelectrodes, namely cathode 302, is cooled. The cathode is in contactwith a separate, channeled cooling body 306 containing at least onechannel 304 through which a flow of cooling medium can be directed inorder to cool the channeled cooling body 306. Since the channeledcooling body is in good thermal contact with the cathode, the flow ofcooling medium will function to remove heat from the cathode. Thechanneled cooling body 306 can be comprised of the same material as theelectrode 302, or can be comprised of any suitable material with asufficiently high thermal conductivity that is capable of being used ina gas discharge laser chamber. The cooling medium can be flowed into thechannel(s) by tubes (not shown) going to the outside of the laserchamber 308. When using a separate, channeled cooling body with one ofthe electrodes, care should be taken to ensure that the proper dischargegap distance is left between the discharge electrodes. Care should alsobe taken to minimize any changes to the flow of laser gas in the chamberas a result of the channeled cooling body.

FIG. 4 shows a cooling approach 400 in accordance with a thirdembodiment of the present invention. This embodiment is similar to theapproach described with respect to FIG. 2, except that only a singleelectrode, here the cathode 402, is cooled. The cooling medium can flowthrough at least one channel 404 in the body of the electrode. Thecooling medium can be flowed into the channel(s) by tubes going to theoutside of the laser chamber 406.

FIG. 5 shows a cooling approach 500 in accordance with a fourthembodiment of the present invention. This embodiment is similar to theapproach described with respect to FIG. 3, in that a single electrode,here the anode 502, is cooled by a separate, channeled cooling body 504in good thermal contact with the anode 502. The channeled cooling body504 has at least one fluid channel 506 through which the cooling mediumcan flow. In this embodiment, however, the cooling channel is disposedaway from the discharge gap and positioned inside the lower, laser gasportion of the laser chamber, wherein the laser gas passes through theheat exchanger and particulate filter as directed by the laser gas fanelement. A flow of cooling medium through such a channel will stillfunction to remove heat from the anode, as the channeled cooling body isin good thermal contact with the electrode, but also will function tocool the laser gas flowing through the lower portion of the laserchamber as directed by the fan element. FIG. 6 shows a cooling approach600 in accordance with a fifth embodiment of the present invention. Inthis embodiment, a single electrode, here the anode 602, is cooled bydirecting a flow of cooling medium directly through the anode throughone or more channels 604 as described with respect to FIG. 2. Thisembodiment can be used in place of the system in FIG. 5, for example,where simplicity is desired and it is not necessary to remove heat fromthe laser gas flowing through the laser chamber.

FIG. 7 shows a cooling approach 700 in accordance with a sixthembodiment of the present invention. In this embodiment, only the anodeelectrode 702 is cooled. The anode electrode 702 is shaped in such a wayas to optimize the flow of laser gas inside the laser chamber 704. Forexample, the anode electrode can generally have a surface contour thatfollows the natural flow of gas through the laser chamber. This flow caninclude the area near the discharge region between the electrodes,through the heat exchangers, past the fan element and electrostaticfilter. The electrode can extend both into the discharge region and intothe lower, laser gas portion of the laser chamber. The electrode canserve to ensure that the flow of gas passes substantially through theheat exchangers, and can extend almost down to the fan element in orderto minimize turbulence and ensure adequate filtering of the laser gas.The electrode body 702 can have at least one channel 706 through which acooling medium can flow, which can be located near the discharge areaand/or in the lower portion of the gas chamber. In fact, many channelscan be provided to enhance control over the cooling of the anodeelectrode. When the electrode body extends beyond the discharge area 712and into the lower, laser gas portion of the laser chamber 704, in thisexample extending almost to the fan element 708, the lower portion ofthe electrode also can function as an additional heat exchanger for thelaser gas, in order to cool the laser gas in the chamber 704. Typically,only a heat exchanger 710 system is used to cool the laser gas. The useof a heat exchanger alone, however, may not provide sufficient heatdissipation for high repetition gas lasers. Additional heat exchangerscan be added to the chamber, but such additional elements will tend toalter the gas flow and reduce the overall gas volume in the chamber.Using an extended, cooled electrode to further cool the laser gas canhelp to provide the necessary heat dissipation for higher repetitionoperation, without disrupting the flow of gas through the laser chamber.

Another advantage to the design of FIG. 7 is that the amount ofelectrode consumption or erosion typically is higher for the anode, suchthat it can be advantageous to cool the anode electrode of the system asshown in FIG. 7, while retaining a level of simplicity by not alsocooling the cathode. The cooling medium can be brought into thechannel(s) 706 of the anode by tubes (not shown) going to the outside ofthe laser chamber. Each channel can be connected to a single flow, oreach channel can receive a separate flow of cooling fluid.Alternatively, since the temperature of the portion of the anode nearthe discharge can be most critical, there can be a first flow of coolingliquid directed to at least one channel near the discharge area, withthe remaining channels utilizing a separate flow of cooling liquid. Itmay be advantageous to use different cooling media for these separateflows. It should be understood, however, that it is also possible tocool the cathode in this embodiment, as described above.

FIG. 8 shows a cooling approach 800 in accordance with a seventhembodiment of the present invention. In this embodiment, only the anodeelectrode 802 is cooled, and the anode 802 is designed to optimize theflow of laser gas similar to the approach described with respect to FIG.7. In this embodiment, however, the outer surface of the anode has afin-like structure 808 designated by the dashed line in the Figure,which corresponds to a surface contour as shown in the cross-section 900of FIG. 9. Such a fin-like structure can be used over the entire surfaceof the electrode 802 in order to improve both the flow of laser gas andthe amount of heat dissipation from the laser gas, as is known with heatexchange technology. The body of the electrode 802 can have at least onechannel 806 through which a cooling medium can flow, such as describedwith respect to FIG. 7. It should be understood that it is also possibleto cool the cathode in this embodiment, as described above.

FIG. 10 shows a cooling approach 1000 in accordance with an eighthembodiment of the present invention. In this embodiment, the laserchamber 1002 is cooled in addition to one of the electrodes, here thecathode electrode 1004. The laser chamber 1002 is cooled through use ofat least one cooling element 1006 in good thermal contact with theexterior of the laser chamber 1002. It should be understood, however,that cooling elements also can be placed along the inside of the laserchamber, preferably in such a way as to minimize the effect on the flowof gas through the chamber. The cathode 1004 can be cooled through useof at least one cooling element 1008 in good thermal contact with acathode plate 1010, which is in good thermal contact with the cathode1004. The temperature of the walls of the laser chamber 1002, as well asthe cathode plate 1010, can be monitored by temperature sensors 1012 and1014, respectively. The temperature sensors used can be any appropriate,commercially available temperature sensors, such as any of the class ofPT-100 temperature sensors known in the art. The temperature sensors canprovide signals to at least one computer or processing unit for thesystem (shown as 168 in FIG. 1(b)), which can be used to regulate thetemperature by sending a signal to the cooling module to adjust theappropriate cooling elements 1006, 1008. Such an approach also can beused with other approaches described elsewhere herein. For example,either the anode or the cathode, or both, can include fluid channels forcirculating a cooling fluid through the respective electrode(s). Also,the anode can have any appropriate shape, such as described with respectto any of FIGS. 3-9.

FIG. 11 shows a cooling system 1100 in accordance with a ninthembodiment of the present invention. In this embodiment the anode 1102is thermally connected to a first cooling plate 1104. The cooling platecan be a single plate or a combination of plates. The cooling plate canhave a first portion that contacts the anode, and a second portion thatextends into the lower, laser gas portion of the laser chamber. Thefirst cooling plate 1104 can have at least one channel 1106 throughwhich a cooling medium can flow, which can be near the discharge area inorder to cool the electrode or in the laser gas portion to act as a heatexchanger for the laser gas, or both. The cooling plate can have a shapewhich facilitates flow of the laser gas in the laser chamber 1108. Forinstance, the cooling plate can be shaped to create an aerodynamicpathway to direct the flow of gas in the chamber in order to minimizeturbulence in the laser chamber. The first cooling plate also canfunction to cool the laser gas as the gas flows through the chamber pastthe cooling plate, such that the typical heat exchanger is notnecessary. To further improve the cooling of the laser gas, a secondcooling plate 1110 can be utilized in the laser chamber, along the flowof laser gas. The second cooling plate also can be a single element or acombination of elements. The surface of each of the cooling plates 1104,1110 can have fins as described with respect to FIG. 9, in order toimprove the dissipation of heat from the laser gas. Fins on an anodesupport section 1112 can enlarge the surface area in contact with thelaser gas, which can help to improve the amount of cooling. Various finshapes are possible that are known from commercial heat sinks. Such finscan be up to 20 mm high in one embodiment, and can have a small crosssection for a low gas flow resistance. An advantage to such anembodiment is that no heat exchangers are required, such as are shown inthe laser chamber of FIG. 1. Removing the heat exchangers not onlysimplifies the overall system, but also can function to reduce theamount of turbulence in the system that otherwise can be caused by thepresence of the heat exchangers. The first and second cooling plates canbe shaped to direct gas flow in the chamber, while leaving openings thatallow the gas to reach the dust precipitator 1114, for example, and toallow the flow of gas to mix with additional gas in the chamber.

It should be recognized that a number of variations of theabove-identified embodiments will be obvious to one of ordinary skill inthe art in view of the foregoing description. Accordingly, the inventionis not to be limited by those specific embodiments and methods of thepresent invention shown and described herein. Rather, the scope of theinvention is to be defined by the following claims and theirequivalents.

1. An excimer or molecular fluorine laser system, comprising: aresonator including therein a laser chamber filled with a laser gasmixture; and a pair of electrodes for energizing said laser gas mixturein order to generate an optical pulse in the resonator, at least oneelectrode of said pair of electrodes having disposed therein a channelcapable of receiving a flow of cooling medium in order to remove heatfrom said at least one electrode.
 2. A system according to claim 1,further comprising: a power supply circuit in electrical communicationwith said pair of electrodes, the power supply circuit providing adriving voltage to said pair of electrodes in order to energize saidlaser gas mixture.
 3. A system according to claim 1, further comprising:a heat exchanger in the laser chamber for removing heat from said lasergas mixture.
 4. A system according to claim 1, further comprising: a gascirculation fan for circulating the laser gas mixture in the laserchamber.
 5. A system according to claim 1, further comprising: a coolingmodule unit in fluid communication with the laser chamber for supplyinga flow of cooling medium to said channel.
 6. A system according to claim5, further comprising: tubing connecting said cooling module unit tosaid channel in order to provide the flow of cooling medium.
 7. A systemaccording to claim 1, further comprising: a media reservoir capable ofstoring said cooling medium.
 8. A system according to claim 1, furthercomprising: a heat exchange unit outside the laser chamber for coolingthe cooling medium.
 9. A system according to claim 1, wherein: at leastone of said pair of electrodes has a shape that extends into a dischargeregion and into a laser gas region of the laser chamber.
 10. A systemaccording to claim 9, wherein the at least one of said pair ofelectrodes extends substantially to a gas circulation fan forcirculating the laser gas mixture in the laser chamber.
 11. A systemaccording to claim 1, wherein: at least one of said pair of electrodeshas a surface including a plurality of fins.
 12. A system according toclaim 1, wherein: said cooling medium is a liquid.
 13. A systemaccording to claim 1, wherein: said cooling medium is gaseous.
 14. Asystem according to claim 1, wherein: said cooling medium is an oil. 15.A system according to claim 1, wherein: said cooling medium is water.16. A system according to claim 1, wherein: said cooling medium is at atemperature in the range of 30-120° C.
 17. A system according to claim1, wherein: said flow of cooling medium is directed through the channelwhen the laser system is operated at a repetition rate of at least 4kHz.
 18. An excimer or molecular fluorine laser system, comprising: aresonator including therein a laser chamber filled with a laser gasmixture; a pair of electrodes for energizing said laser gas mixture inorder to generate an optical pulse in the resonator; and a coolingelement in thermal contact with at least one electrode of said pair ofelectrodes, the cooling element capable of removing heat from said atleast one electrode.
 19. A system according to claim 18, furthercomprising: an electrode plate positioned between the cooling elementand the at least one electrode in order to provide said thermal contact.20. A system according to claim 18, wherein: the cooling element islocated outside the laser chamber.
 21. A system according to claim 18,wherein: the cooling element has at least one channel disposed thereinfor receiving a flow of a cooling medium in order to remove heat fromthe cooling element.
 22. A system according to claim 18, furthercomprising: a temperature sensor in thermal contact with the at leastone electrode.
 23. A system according to claim 22, further comprising: acooling module capable of receiving a temperature signal from thetemperature sensor and controlling a heat removal capacity of thecooling element in response to the temperature signal.
 24. A systemaccording to claim 18, further comprising: a power supply circuit inelectrical communication with said pair of electrodes, the power supplycircuit providing a driving voltage to said pair of electrodes in orderto energize said laser gas mixture.
 25. A system according to claim 18,further comprising: a heat exchanger in the laser chamber for removingheat from said laser gas mixture.
 26. A system according to claim 18,further comprising: a gas circulation fan for circulating the laser gasmixture in the laser chamber.
 27. A system according to claim 23,further comprising: tubing connecting said cooling module unit to saidchannel in order to provide the flow of cooling medium.
 28. A systemaccording to claim 18, further comprising: a media reservoir for storingsaid cooling medium.
 29. A system according to claim 18, furthercomprising: a heat exchange unit outside the laser chamber for coolingthe cooling medium.
 30. A system according to claim 18, wherein: thecooling element is located in a laser gas region of the laser chamberand extends substantially toward a cooling fan element in the laser gasregion.
 31. A system according to claim 18, wherein: said coolingelement is disposed inside the laser chamber.
 32. A system according toclaim 31, wherein: the cooling element is shaped to direct a flow of thelaser gas mixture past heat exchange elements located in the laser gasregion.
 33. A system according to claim 31, wherein: said coolingelement has a surface that includes a plurality of fins.
 34. A systemaccording to claim 18, wherein: said cooling medium is selected from thegroup consisting of liquids, gases, and oils.
 35. An excimer ormolecular fluorine laser system, comprising: a resonator includingtherein a laser chamber filled with a laser gas mixture; a pair ofelectrodes for energizing said laser gas mixture in order to generate anoptical pulse in the resonator, at least one electrode of said pair ofelectrodes having disposed therein a channel capable of receiving a flowof cooling medium in order to remove heat from said at least oneelectrode; a temperature sensor in thermal contact with the at least oneelectrode and capable of generating a temperature signal; and a coolingmodule for providing the flow of cooling medium, the cooling modulecapable controlling the flow of cooling medium through the channel inresponse to the temperature signal in order to regulate a temperature ofthe at least one electrode.
 36. A system according to claim 35, furthercomprising: a power supply circuit in electrical communication with saidpair of electrodes, the power supply circuit providing a driving voltageto said pair of electrodes in order to energize said laser gas mixture.37. A system according to claim 35, further comprising: a heat exchangerin the laser chamber for removing heat from said laser gas mixture. 38.A system according to claim 35, further comprising: a gas circulationfan for circulating the laser gas mixture in the laser chamber.
 39. Asystem according to claim 35, further comprising: tubing connecting saidcooling module to said channel in order to provide the flow of coolingmedium.
 40. A system according to claim 35, further comprising: a mediareservoir for storing said cooling medium.
 41. A system according toclaim 35, further comprising: a heat exchange unit outside the laserchamber for cooling the cooling medium.
 42. A system according to claim35, wherein: said cooling medium is selected from the group consistingof liquids, gases, and oils.
 43. A system according to claim 35,wherein: the at least one electrode has a surface including a pluralityof fins.